Shared ip address most likely. With which someone else is triggering the captcha. Or even a range of ips which are or have been allocated to someone else.
I imagine the solution should come about as follows.
Customers complain about captchas and seek alternative isps.
Someone else provides better connections without tainted ip addresses (without sketchy customers)
OR, the current isp decides to crack down on customers who are being labeled as abusive. Problem solved.
Someone is likely providing cheap internet to sketchy people, who taint the experience for other users. It is on them to crack down and stop selling to sketchy users. Ban their payment methods/identities, so cloudflare doesn't have to ban ips.
I imagine the solution should come about as follows.
Customers complain about captchas and seek alternative isps.
Someone else provides better connections without tainted ip addresses (without sketchy customers)
OR, the current isp decides to crack down on customers who are being labeled as abusive. Problem solved.
Someone is likely providing cheap internet to sketchy people, who taint the experience for other users. It is on them to crack down and stop selling to sketchy users. Ban their payment methods/identities, so cloudflare doesn't have to ban ips.